Optical glass



Aug. 12, 1952 w. H. ARMISTEAD 2,606,341 OPTICAL GLASS Filed May 31, 1949,

'INVENTOR. M; 4 /AM ARM/annex:

ATTORNEY Patented Aug. 12, 1952 QPTICAL GLASS 7 William H. Armistead, Corning, N. Y., assignor to Corning Glass Works, Corning, N.

ration of New York Y., a corpo- Application May 31, 1949, Serial N 0. 96,285

1 V This application is a continuation in part of my pending application Serial No. 627,746 filed November 9, 1945, since'abandoned, which in turn is a continuation in part of my application Serial No. 614,288 filedseptember 4, 1945, now Patent Number 2,435,995, and relates to optical glass compositions which have an index of refraction for the D line (nD) greater than 1.60 and which are suitable for use in optical instruments and devices of various kinds. t

Heretofore the mostcommon optical glasses having a refractive'index greater than 1.60 have been the flint glasses having a high lead content and the dense bariumicrown glasses. For some purposes it is desirable, to use a glass which not only has a refractive index in the range 1.7 to 1.9 but which has also a high dispersive index (u) or nu value, as it is sometimes called; 5

The flint glasses have relatively low dispersive indices which decrease as their lead contents and refractive indices are increased.

The barium crown glasses in general have high dispersive indices, but their refractive indices do not exceed about 71.63 because an increase in the barium content beyond this point, about 50% BaOyresults in devitrification of the glass when it is slowly coole'dpr reheated for molding. Although a barium content of 55-70% BaO was heretofore desirable, it could not be attained without devitrification of the glass. The primary object -of this invention is toprovide-transparent optical glasses which have refractive indices (nDlgreater than 1.60 anddispersive indices (v) higher than have heretofore been obtainable in the flint glasses.

Another object is to provide barium crow glasses which contain over 50% and up to 70% BaO and which will not devitrify when reheated or slowly cooled. '7

Another object is to prevent the devitrification of barium glasses having barium contents above 50% BaO.

Another object is to provide glasses which have refractive indices greater than 1.60 and correspondingly high dispersive indices and which have a total of at least 40% B20 and CdO.

I have found that the introduction of substantial amounts of CdO into dense barium crown glasses enables the barium content to be increased to as much as about 70% ;BaO without dissolve.

8 Claims. (01. 10e-s2) total BaO and Edd content be not, less than 40%,withthe minimum amount of each being 3%. The'glasses must 'contain at least one and preferably both of the glass-forming oxides SiOz and B203, either one or both of which must amount to at least' 12% but neither 'or both of which should exceed about By the term"glass forming oxide'-I meanan oxide which, when molten, can'be cooled to form a glass of and by itself.

The new glasses comprise essentially BaO, CdO and either. SiO2 orxBzOs or, both SiOz and B203 in the proportions, stated above. Minor amounts of other constituents may also be present in a total up to about 30% without substantial change in the desirable properties of the glasses, subject to the following considerations: The glasses preferably should contain at least one. of the refractory .ox'ides A1203 or ZrOz, bothof Which aid in preventing. devitrification; 'ZrOz'also helps to raise both the refractive index and the. dispersive index butshould not exceed about 10% on account of itsiilowssolubility. -;Al2Os': alone may amountto as'imuch. as .'30%,-but, must be less when ZrOz is present in'or'derthat the latter may The presenc'eof PbO in amounts as high as 30% and/or alkali metal oxide, n amely, LizQ, NazO, K2001: mixtures thBIEOfylll amounts upto 12.0% is; also advantageous for stability and opticalproperties; Either; alkali metal oxide or A1203, or both, should be. present in the absence of BzOsto replace the fiuxing power of the latter. Other oxides which are commonly used in optical glass compositions such as, for example, BeO, ZnO, AszOaisbzoa orTiOzjmay also be included in the new glasses, but-,preferably'should not exceed a total of about 5%'.-

The following glasses, which are given in percent by weight as calculated from their respective A B C D E I The above glasses are chemically stable and resistant to devitrification. It will be noted that they have refractive indices greater than 1.60 and relatively high dispersive indices. Glass E is particularly suitable for ophthalmic lenses.

To illustrate the relationship between nD and v for the glasses of this invention, reference is had to the accompanying drawing which is a diagram representing the values of 221) for the above glasses plotted against their respective values of v and. designated by the letters of the respective glasses. It will be noted that the values for the various glasses are above the lines X and Y which represent the approximate minima in the values for TD and v which characterize the glasses of this invention.

The line X is drawn through the points ('nD=1.60, 11:42), and (nD=1.70, 12:32) and is defined by the equation The line Y is drawn through the points (nD=1.70, 1 :32) and (nD=1.85, 11 25) and is defined by the equation p=11l.4-46.6nD

essentially 3% to 70% BaO, 3% to 75% CdO, and

12% to 50% of a mixture of SiOz and B203, the total BaO, CdO, SiOa and B203 being at least 70%, the total BaO and CdO being at least 40%, and A1203 in an amount up to 30%, the remain- 3. A transparent optical glass which comprises essentially 3% to 7 BaO, 3% to 75% CdO, and 12% to 50% of a mixture of Si02 and B203, the total BaO, CdO, SiOz and B203 being at least 70%, the total 390 and CdO being at least 40%, and an alkali metal oxide in an amount up to selected from the group consisting of LizO, Na2O, K20 and mixtures thereof, the remainder of the composition comprising compatible oxides, the refractive index (12D) being at least 1.60 and the dispersive index (12) being greater than both v=ZO2-1OUTLD and v=11l.446.6nD..

4. A transparent optical glass which comprises essentially 3% to 70% BaO, 3% to 75% CdO, and 12% to 50% of a mixture of Si02 and B202, the total BaO, CdO, S102 and B203 being at least 70%, the total BaO and CdO being at least 40%, and A1203 in an amount up to and an alkali metal oxide in an amount up to 20% selected from the group consisting of L120, NazO, K20 and mixtures thereof, the remainder of the composition comprising compatible oxides, the refractive index (nD) being at least 1.60 and the dispersive index (11) being greater than both v=202-1DO1ZD and 5. A transparent optical glass which comprises essentially 3% to 70% BaO, 3%to 75% Q10, and 12% to 50% of a mixture of S102 and B202, the total BaO, CdO, S102 and B203 being at least 70%, the total BaO and CdO being at least and PbO in an amount up to 30%, the remainder of the composition comprising compatible oxides, the refractive index (721)) being at least 1.60 and the dispersive index (1 being greater than both v=202-100nD and v=111.4:46.61LD.

6. A transparent optical glass which comprises essentially 3% to 70% BaO, 3% to 75% CdO, and 12% to of a mixture of SiOz and B203, the total BaO, CdO, Si02 and B203 being at least the total BaO and CdO being at least 40%, and PhD in an amount up to 30% and A1203 in an amount up to 30%, the remainder of the composition comprising compatible oxides, the refractive index (111)) being at least 1.60 and the dispersive index (1') being greater than both 11:202-100121) and v:111.4-46.612D.

7. A transparent optical glass which comprises essentially 3% to 70% BaO, 3% to CdO, and 12% to 50% of a mixture of SiOz and B203, the total BaO, CdO, S102 and B203 being at least 70%, the total Ba() and CdO being at least 40%. and 2102 in an amount up to 10%, the remainder of the composition comprising compatible oxides, the refractive index 011D) being at least 1.60 and the dispersive index (2) being greater than both v=202-nD and v=11l.4-46.6nD.

8. A transparent optical glass which consists approximately of 50% BaO, 12% CdO, 10% A1203, 3% B203, 19% SiO2, and 1% Na20, on an oxide basis as calculated from the batch and which has a refractive index (nD) of approximately 1.653 and a dispersive index (11) of approximately 50.6.

WILLIAM H. ARMISTEAD.

file of this patent:

UNITED STATES PATENTS Name Date Pincus Aug. 2, 1949 der of the composition comprising compatible oxides, the refractive index (nD) being at least 1.60 and the dispersive index (1 being greater than both v=202-1001LD and v=111.446,6n.D.

Number 

1. A TRANSPARENT OPTICAL GLASS WHICH COMPRISES ESSENTIALLY OF 3% TO 70% BAO, 3% TO 75% CDO, AND 12% TO 50% OF A MIXTURE OF SIO2 AND B2O3, THE TOTAL BAO, CDO, SIO2 AND B203 BEING AT LEAST 70%, THE TOTAL BAO AND CDO BEING AT LEAST 40%, AND THE REMAINDER OF THE COMPOSITION COMPRISING COMPATIBLE OXIDES, THE REFRACTIVE INDEX (ND) BEING AT LEAST 1.60 AND THE DISPERSIVE INDEX (V) BEING GREATER THAN BOTH V=202-100ND AND V=11,1.4-46.6ND. 